In diagnosis of stomach cancer, detection of cancer cells in lymph nodes (diagnosis of lymph node metastasis) becomes information useful for determining operation range or for determining postoperative chemotherapy. At present, diagnosis of lymph node metastasis is carried out by a medical pathologist by tissue diagnosis with a frozen section or paraffin section of lymph node tissue (for example, HE (hematoxlylin-eosin) staining method, IHC (immunohistochemical method), etc.). However, even if cancer cells are present in lymph nodes, the cancer cells will be overlooked if a section is prepared from a cancer cell-free cut surface and the section is subjected to tissue diagnosis. In addition, diagnosis results may vary depending on the level of skill of a medical pathologist who makes the diagnosis.
Under these circumstances, studies on molecular diagnosis of cancer by LAMP (loop-mediated isothermal amplification method) and PCR (polymerase chain reaction) have been extensively conducted. Molecular diagnosis can be carried out by detection of molecular markers (for example, a protein expressed specifically in a cancer cell, a gene encoding the protein or an mRNA of the gene).
A wide variety of proteins have been expressed in stomach cancer cells, and molecules capable of serving as stomach cancer markers have been extensively searched.
For example, JP-A 2006-223303 describes that the expression levels of genes for TFF1, TFF2, FABP1, CK20, MUC2, CEA, TACSTD1, MASPIN, PRSS4, GW112 and ACTB are examined in KATOIII cells, a cell line derived from human stomach cancer, or in cells in an intraperitoneal irrigation solution collected from a stomach cancer patient, and that reappearance of stomach cancer is predicted on the basis of the expression levels of these genes.
JP-A 2006-526998 describes a method of diagnosing stomach cancer by measuring the expression levels of genes for EEFA1A, TUBA6, FKBP1A, PKM2, LDHA, RPL4, ARF1, SURF4, KRT8, GAPD, HSPCB, PGK1, HMGIY, K-ALPHA-1, FTH1, HSPA8, SH3GLB2, ACTB, HSPCA, TMSB4X, PYCR1, ATF4, JUN, HSPB1, IGKC, SNC73, CD74, LOC131177 (FAM3D), AGR2, and IMAGE:4296901 (pepsin A). It also describes a method of diagnosing metastatic stomach cancer by measuring the expression levels of genes for GADD45B, JUN, HMGIY, GSTP1, LMNA, ESRRA, PLK, CD44, IGFBP3, PKM2, FKBP1A, KRT8, TMSB4X, GAPD, ATP5A1, PTMA, CALM2 and NET1.
JP-A 2005-304497 describes that stomach cancer can be diagnosed on the basis of the expression levels of genes for PVT1, MYC, FOLR1, PLUNC (LUNX), E2F1, TGIF2, TNFRSF5, NCOA3, ELMO2, MYBL2, NCOA3 (AIB1), PTPN1, PRex1, BCAS1, ZNF217, STK6 (BTAK), CUL4B, MCF2, CTAG, SDC1, DNMT3A, MLH1, CTNNB1, CCK, ZNF131, CDK6, MET, MYC, PVT1, EGR2, KSAM (FGFR2), PKY (HIPK3), LMO2, CD44, KRAS, KRAG (SSPN), CYP1A1, IQGAP1, FURIN (PACE), PPARBP, ERBB2, CCNE1, MYBL2, BAIAP1, PTPRG, N33, TEK, MTAP, CDKN2A (p16), MLLT3, JAK2, GASC1, D9S913, SMAD4, MADH2, MADH7 (SMAD7), DCC, MALT1, GRP, BCL2, FVT1, SERPINB (PI5) and CTDP1.
However, the expression levels of the above genes in lymph node cells recognized to have metastasis of stomach cancer-derived cancer cells and in normal lymph node cells were not confirmed in any of the above patent literatures. Accordingly, it is not clear which of the genes enumerated in the literatures supra are useful as markers for judging lymph node metastasis of stomach cancer.
As molecular markers for judging lymph node metastasis of stomach cancer (also referred to hereinafter as simply “markers”), human carcinoembryonic antigen (CEA) and cytokeratin 20 (CK20) have been reported (Keisuke Kubota et. al., “Quantitative detection of micrometastases in the lymph nodes of gastric cancer patients with real-time RT-PCR: a comparative study with immunohistochemistry”, International Journal of Cancer, May 2003, Vol. 105, pages 136-143).